Composite punch for powder compacting press and the like

ABSTRACT

A composite punch for powder compacting presses of the type preferably using a plurality of such punches in a common tool holder. The composite punch of the invention has a cylindrical body member provided with a longitudinal bore in one end of which is press-fitted a punch member. The other end of the cylindrical body member is press-fitted in a bore centrally disposed in a disk defining the portion of the composite punch for mounting in the punch holder. The three elements forming the composite punch are preferably made of a carbide material, and both the punch member and the cylindrical body member are provided with a reduced outer diameter at each end press-fitted in the other element.

United States Patent 1151 3,682,577 Smith 1451 Aug. 8, 1972 COMPOSITE PUNCH FOR POWDER 3,279,297 10/ 1966 Smiltneek ..83/698 COIVIPACTING PRESS AND THE LIKE 1,166,613 l/1916 Mackle ..83/698 X [72] Inventor: E. Snuth, Blrmmgham, Primary ExaWner Andrew'R Juhasz Assistant Examiner-Leon Gilden [73] Assignee: Pentronix, Inc., Lincoln Park, Mich. Attorney-Hauke, Gifford and Patalidis [21] Appl' 785584 A composite punch for powder compacting presses of the type preferably using a plurality of such punches 52 0.8. Ci. ..425/7s, 72/354, 425/412 i a eennnen tee! l The composite Punch f the 51 Int. Cl ..B29C 3/00 lnvenhen has a eyhndneel y member Prevlded [58] Field of Search ..72/354; 18/165, 16 M; with a longitudinal bore in one end of which is e- 287/203 126 fitted a punch member. The other end of the cylindrical body member is press-fitted in a bore centrally 56 R f C-ted disposed in a disk defining the portion of the com- 1 e erences posite punch for mounting in the punch holder. The UNITED STATES PATENTS three elements forming the composite punch are 2 332 704 10/1943 Enes et al 72/354 prefegably i f; f i gfg and 2? punc mem ran ecym r10 0 ymem rare U schmann provided a reduced outer diameter at each d 222? press-fitted in the other element. 45s:076 8/1891 Simmons ..83/698 x 6 Claims, 5 Drawing Figures 2 PATENTEDAUB 8 [972 3,682.57?

FIGS INVENTOR JOSEPH E. SMITH i PRIOR ART ATTORNEYS COMPOSITE PUNCH FOR POWDER COMPACTING PRESS AND THE LIKE CROSS REFERENCE TO RELATED APPLICATIONS The present application is related to application Ser. No. 767,648, filed on Oct. 15, 1968 in the name of Joseph E. Smith, Jr., and Georges E. DeTroyer and entitled Tool Set for Powder Compacting Press now US. Pat. No. 3,561,056, issued Feb. 9, 1971. The present application is also related to issued US. Pat. Nos. 3,328,840, 3,328,842, 3,344,213, 3,414,940, and 3,415,142.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the field of punch assemblies for powder compacting presses and the like, although it will be appreciated that the particular punch construction of the invention has also substantial usefulness in punch constructions for pressing or punching metallic or non-metallic sheet materials.

2. Description of the Prior Art Powder compacting presses and the like machines utilize one or several punch members each disposed at the bottom of and displaceable in a cavity which has been filled with loose powder material to be compacted to an appropriate shape, generally in the shape of a cylinder, disk or toroid. The loose powder material is compacted between the end of the punch member and the end of a counter-punch or, alternately as disclosed in the hereinbefore referred to patents and application, between the end of the punch member and an anvil arranged to be displaceable over the die cavity for closing the open end thereof. Each punch may be individually actuated by an actuating mechanism or the punches may be disposed in a cluster and held by a common punch holder so as to be simultaneously and jointly displaceable, each punch member being disposed within an individual die cavity. The common punch holder holding a plurality of punches has preferably, as also disclosed in the hereinbefore mentioned patents and application, a punch holding head provided with a circular groove adapted to accept an enlarged diameter end portion of the punch, the projecting body portion of the punch being disposed within a radial slot extending all the way from the top surface of the punch holding head of the holder to the circular groove.

FIGS. 1 through 4 are well representative of the prior art punch constructions, wherein at least the working end of the punch is adapted to slidably engage the inner bore of a die bushing. Both the punch member and the die bushing are preferably made of an ultra hard material, for example a cemented carbide of a metal such as tungsten, titanium or the like, to insure appropriate rigidity, sturdiness, resistance to compression, and resistance to wear of the working portions of the punch and die.

The punch assemblies of FIGS. l-4 are examples of construction best adapted to provide punches for compacting magnetic memory cores from ferrite powder and the like. A magnetic memory core is generally in the form of a toroid, a few thousandths of an inch in diameter, having a central aperture for the threading therethrough of wires when a plurality of finished sintered cores are disposed in an appropriate frame so as to form a magnetic memory plane or the like. Magnetic memory cores were formally of a substantial size, in the order of 80 mils in diameter, but the size has been continuously and consistently decreased over the years following a trend towards miniaturization and faster response of magnetic core memory stacks. Magnetic cores of 25, 20 and 18 mils are currently being manufactured, and the trend is still toward further miniaturization aiming at magnetic core sizes of only l6, l2 and even 8 mils or less. It is obvious that such a trend toward miniaturization of magnetic cores renders more critical the precision with which ferrite compacting presses and tooling must be built. Hollow punches having a precise O.D. dimension of 0.012, 0.008, or 0.006 in., with a wall thickness from 0.001 to 0.0005 in., and made of an ultra hard material such as a carbide or the like, require precise manufacturing apparatus and techniques, and delicate and precise instrumentation for checking the finished cores. The precision of fit between the punch outer diameter and the die bushing inner diameter must be held within 0.00005 in., and such a precision must be maintained over the life of the punch so as to provide constant density and dimensional precision of the pressed cores.

A further complication in manufacturing punches for ferrite compacting operations is due to the substantial length of the punch which results in a slender part which may easily break due to the brittleness of the material with which it is made, when subjected to uneven or bending stresses. Consequently, the punches must be precisely mounted in an appropriate holder, and high precision is required in the fitting between the holder and the punch supporting means therein. Concentricity of the longitudinal bore through the punch and high precision in the dimension of the inner diameter of such bore, permitting passage therethrough of the core rod, are also essential.

The prior art has attempted to solve the many problems presented by the aforementioned require-v ments for satisfactory punch construction for ferrite compacting machines, but without too much success to date. Some aspects of the prior art evolution are schematically illustrated in FIGS. 1-4 therein for the sake of better appreciation of the advantages conferred by the present invention.

As disclosed, for example, in the aforesaid patents and application, a plurality of identical punch assemblies are mounted on the end of a common holder and are disposed preferably in a circular arrangement on the enlarged end of the holder for reciprocation in unison by such holder driven by an appropriate ram forming part of the press mechanism, part of the end of each punch being engaged continuously in the bore of a die bushing supported in an appropriate die plate on the press. The space in the die bore above each punch end is filled with a predetermined amount of powder propriate pickup means to pick up the compacted cores.

Referring more particularly to FIG. 1, there is schematically illustrated a typical example of prior art punch assembly, designated generally at 10, a plurality of which is mounted on the enlarged end 14 of a common punch holder 12 in a circular groove 16 adapted to accept and enlarged diameter portion 18 formed integral with the punch body portion 20 of each punch assembly. A radial slot 22 is disposed in the enlarged portion 14 of the holder 12 in such manner as to afford clearance along the punch body 20 of each punch assembly, and all the punch assemblies are locked in position by means of an annular locking ring 24, the combined thickness of the locking ring 24 and of the enlarged portion 18 of the punch body 20 being substantially equal to the height of the groove 16. In this manner, all the punch assemblies are held longitudinally with precision, but they are permitted to float radially so as to be each self-centering in the bore 26 of the die bushing shown in phantom line at 28. Each punch assembly is made of two assembled separate elements including, in addition to the punch body 20 having an integral enlarged diameter mounting portion 18, a punch member 30 preferably made of carbide or like material, while the punch body 20 is preferably made of steel or like material. The punch member 30 is made with precision relatively to its outer diameter dimensions. It is a cylinder as perfect as high quality precision grinding machines permit to achieve, and it has a precise longitudinal bore 32 for passage therethrough of a preferably stationary core rod 34. The core rod 34 is also made of a material such as a cemented carbide and its end 35 projecting beyond the end of the punch member 30 defines acore disposed within the die bore 26 for forming the central aperture in the toroidal compacted article. The lower end of the core rod 34 is held by means, not shown, permitting precise longitudinal adjustment of the position of the upper end of the core rod and free radial floating of the core rod such that it is self-centering within the bore 32, in the same manner as the punch member 30 is selfcentering within the bore 26 in the die bushing 28. A longitudinal bore 36 is disposed in the punch body 20 so as to afford passage therethrough to the core rod 34.

The punch member 30 is press-fitted in an enlarged diameter counterbore portion 40 of the bore 36 in the punch body 20, such enlarged diameter bore portion 40 forming an annular abutment 42 for the lower end face 44 of the punch member 30. The counterbore forming the enlarged diameter bore portion 40 must evidently be machined with precision, so as to insure an adequate fit between the inner surface of theenlarged bore portion and the outer surface of the punch member 30 engaged therewith, and it will be obvious to those skilled in the art that great difficulties are encountered in boring such counterbore with high precision and in providing sharp corners between the bore surface and the annular abutment surface 42.

Considerable precision is also required in machining the enlarged diameter annular portion 18 of the punch body member 20 such that the thickness of the annular portion be precisely determined and that the surfaces engaged with the bottom surface of the tool holder groove 16 and with the lower surface of the annular locking ring 24 be fiat, parallel to each other and in planes at right angle to the axis of the punch assembly 10. For these reasons, the prior art found it preferable to machine and precisely grind an annular lower face and an annular upper face, designated respectively at 46 and 48, on the enlarged flange-like annular portion 18 of the punch body 20, the remaining of the upper and lower surfaces being undercut, as shown at 50 and only gradually lost but, in addition, the repeated impacting forces transmitted through the rigid punch member cause a repeated hammering to be exerted by the end face 44 of the punch member upon the annular abutment surface 42 of enlarged bore 40 in the punch body 20 which in turn causes the relatively soft metal of the punch body 20 to flow in such manner as to form a ridge, as shown at 54in FIG. 3, in the shape of a radially projecting burr which engages the periphery of the core rod with such force that the punch assembly freezes upon the core rod, with resulting breakage of the punch or core rod.

The prior art has attempted to remedy some of the disadvantages of the punch assembly construction of FIG. 1 ennumerated hereinbefore by way of the construction schematically illustrated at FIG. 2. The arrangement of FIG. 2 consists of a punch assembly 10 having a punch member 30 of somewhat increased length and having its lower end engaged in a deeper enlarged diameter counterbore 40 on the end of the longitudinal bore 36 of the punch body 20. A portion of the enlarged bore portion 40 is further enlarged as shown at 56 so as to create a space around part of the periphery of the punch member 30 where it is disposed within the enlarged bore 40, and that space is filled with an appropriate adhesive or bonding material such as epoxy or the like, as shown at 58. Such a coristruction has resulted in some improvement but has not completely eliminated the settling problem which finally takes place, even though it takes place at a later date. The arrangement of FIG. 2 has consequently only succeeded in providing punch assemblies having a slightly prolonged life span, at the cost of an additional machining operation and an additional assembly step, resulting in increased manufacturing costs, still further increased by the increased cost of the material of the punch member 30 due to the increased length thereof, and by the further complications in obtaining precised outer diameter dimensions of the punch member all along the length thereof, in grinding the precise bore 32 therein to exact dimensions and to precise concentricity relatively to the outer diameter surface. As an alternate to using a bonding agent such as epoxy or the like, as shown at 58, brazing of the punch member 30 to the punch body 20 has also been attempted, but the heat of the brazing operation stresses the components and causes structural distortion such that the accuracy of assembly is destroyed and that a substantial number of punch assemblies must be scrapped.

As a further effort in attempting to eliminate some of the hereinbefore mentioned disadvantages, punches have also been made according to the prior art in the form of the integral punch construction illustrated at 11 at FIG. 4, wherein the punch member 30, the punch body and the enlarged diameter support portion 18 are made integrally of one solid piece of metal carbide or the like. Such a construction eliminates the settling problem but considerably increases the cost of manufacturing the punch assembly, starting from a solid blank having an outer diameter at least equal to the diameter of the enlarged portion 18 thereof. Drilling of the aligned bores 36 and 32 is a difficult and lengthy operation, and the finishing of the outer diameter of the punch section 30 concentric to the axis of the inner bore 32 is a somewhat delicate operation, specially in a structure as illustrated at FIG. 4 wherein the diameter of the bore portion 36 is slightly greater than the diameter of the bore 32. Integral punch assemblies, as illustrated at 11 in FIG. 4, and the punch member portions 30 of the built-up assemblies of FIGS. 1 and 2, are ground on their outer diameter surface from the center axis reference as defined by a rigid wire having an outer diameter exactly matching the size of the bore 32 and passed through the bore. All the external grinding operations are effected by holding the punch by means of such a wire, and it can be seen that the bore 32, even if it extends the whole length of the punch assembly 1 1, must be close to perfect in order to obtain close to perfect concentricity and exact dimension for the outer diameter of the punch section 30. Furthermore, the axis of bore 32 is the reference axis with respect to the angular precision at which are ground the annular surfaces 46 and 48 on the enlarged diameter integral portion 18 of the punch.

SUMMARY OF THE INVENTION The present invention relates to a build-up punch assembly comprising only three separate elements which are relatively easy to manufacture individually and which, in assembly, provide a durable, relatively low cost, rigid tool, permitting to overcome the disadvantages and inconveniences of the prior art as explained hereinbefore.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1-4, as hereinbefore explained represent typical examples of prior art punch assembly constructions for powder compacting presses; and

FIG. 5 is a schematic sectional view of an example of a punch assembly for powder compacting presses, made according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to FIG. 5, an example of punch assembly 100, according to the present invention, consists of three separate elements forming respectively a cylindrical tubular punch body 110, a tubular cylindrical punch member 112 and a disk member 114, each of the elements being separately machined to a relatively high degree of precision. The cylindrical punch member 112 has a reduced diameter portion on one end thereof, as shown at 116 having dimensions adequate to insure press-fit into the longitudinal bore 118 in the cylindrical punch body 110. The reduced diameter portion 116 of the punch member 112 merges into the remaining normal diameter portion 120 of the punch member 112 by way of a radiused abutmentforming section 122, the end of the bore 118 in the punch body 1 10 being provided with a correspondingly radiused edge section 124. The difference in dimensions between the inner bore 118 of the punch body 1 10 and the reduced diameter portion 1 16 of the punch member 112 is of the order of 0.001 in. to insure adequate press-fit of the reduced end of the punch member 112 into the bore 118, the diameter of reduced diameter portion 116 being larger by that amount than the inner diameter of longitudinal bore 118. At least the punch member 112, but preferably both the punch body and the punch member 112 are made of an ultra hard material such as a carbide or the like.

The end of the punch body member 1 l0 opposite the end in which is press-fitted the reduced diameter portion 116 of the punch member 112 is also provided with a reduced diameter portion 126 for press-fit into a substantially central bore 128 in the disk member 114, the disk member 114 being also made preferably of ultra hard material such as carbide or the like. The reduced diameter portion 126 of the punch body 110 has a surface which merges into the normal diameter portion 130 of the body member 110 according to a radiused shoulder abutment 132, a corresponding radiused edge 134 being formed in the end of the bore 128 in the disk 114. The reduced diameter portion 126 of the punch body 110 is press-fitted into the central bore 128 in disk 114 such that the respective radiused shoulder abutments 132 and 134 engage each other.

The separate elements are individually made and are assembled together in an appropriate fixture insuring adequate alignment of the elements and squareness of the assembly. It can be seen that the manufacture of the punch member 112 requires no complicated machining operations, and that the dimensions, straightness and roundness of the main outer diameter portion thereof can be easily obtained and determined from its axial reference as defined by a rigid wire passing through the longitudinal bore 136 thereof, such that the reduced diameter surface grinding operations of the reduced diameter portion 116 is also effected relatively to the axis of the punch member as materialized by such wire, in accurate concentricity relatively to the longitudinal axis of the punch member 112. Although such grinding of the two different outer diameters of the outer surface of the punch member 1 12 must be effected with precision, it will be appreciated by those skilled in the art that it is a relatively simple operation to obtain precise outer diameter dimensions of a cylindrical part, as contrasted to attempting to machine with precision an enlarged diameter portion of an internal bore, as is required in the constructions of the prior art, such as illustrated at FIG. 1 and FIG. 2.

The cylindrical tubular punch body member 110 of FIG. 5 is manufactured in the same manner as the punch member 112, it being obvious however that the dimensions of the principal diameter surface 130 need not be obtained with great precision, as contrasted with the reduced diameter portion 126 adapted to be pressfitted within the central bore 128 of the disk member 114. However it is important that the reduced diameter portion 126 be concentric with the axis of the longitudinal bore 118 in the punch body 110 and that the peripheral surface of the reduced diameter portion be accurately cylindrical.

The disk member 114 needs not have a precisely defined outer diameter, but the central bore 128 therein has a relatively precise dimension so as to insure proper press-fit with the reduced diameter portion 126 of the punch body 110. The axis of the central bore 128 in the disk member 114 must also be substantially precisely at right angle relatively to the annular surfaces 138 and 140 thereof, and the distance separating the two annular surfaces 138 and 140 may be deter mined with precision by grinding on a surface grinder or the like. There is no need in the assembly of FIG. to provide the disk member 1 14 with undercut portions as are required in the embodiments of the prior art.

The arrangement of FIG. 5 provides a punch assembly 100 which is not only much easier to manufacture and assemble than prior art punch assemblies, which is not subjected to settle during use as is the case for the prior art arrangements of FIGS. 1-2, but which also may be salvaged in the event that the punch member 112 becomes worn beyond usefulness or is broken. The damaged punch member 112 is pressed from assembly with the body member 110, and a new punch member 112 is press-fitted in position.

Having thus described the invention by way of a typical example thereof given for illustrative purpose only and not in a limiting sense, what is claimed as new and sought to be protected by United States Letters Patent is as follows:

1. A composite punch comprising a cylindrical body member having a longitudinal bore of uniform cross section throughout its length, a punch member made of a carbide of at least one metal and having a predetermined outer diameter, and a reduced outer diameter portion at one end of said punch member, an end face formed on said reduced outer diameter portion, said reduced outer diameter portion having a length less than the length of said body member bore and being press-fitted in an end of said bore in said body member whereby said end face is spaced from the end of said body member bore out of engagement with said body member, said reduced outer diameter portion blending into said predetermined outer diameter and defining a radiused shoulder portion for engagement with a corresponding radiused portion on the end of said bore in said body member.

2. The punch of claim 1 further comprising a longitudinal bore in said punch member substantially aligned with the bore in said body member.

3. The punch of claim 1 further comprising a disk member, a substantially central bore in said disk member, a reduced outer diameter portion at one end of said body member opposite the end thereof receiving said punch member, said reduced diameter portion of said body member being press-fitted in an end of said lif iiififirl ii ii iein said reduced outer diameter portion of said body member peripherally defines on said body member a radiused shoulder portion for engagement with a correspondingly radiused portion on an end of said bore in said disk member.

5. The punch of claim 1 wherein said punch member and said body member are made of a carbide of at least one metal.

6. The punch of claim 3 wherein said punch member, said body member and said disk member are made of a carbide of at least one metal. 

1. A composite punch comprising a cylindrical body member having a longitudinal bore of uniform cross section throughout its length, a punch member made of a carbide of at least one metal and having a predetermined outer diameter, and a reduced outer diameter portion at one end of said punch member, an end face formed on said reduced outer diameter portion, said reduced outer diameter portion having a length less than the length of said body member bore and being press-fitted in an end of said bore in said body member whereby said end face is spaced from the end of said body member bore out of engagement with said body member, said reduced outer diameter portion blending into said predetermined outer diameter and defining a radiused shoulder portion for engagement with a corresponding radiused portion on the end of said bore in said body member.
 2. The punch of claim 1 further comprising a longitudinal bore in said punch member substantially aligned with the bore in said body member.
 3. The punch of claim 1 further comprising a disk member, a substantially central bore in said disk member, a reduced outer diameter portion at one end of said body member opposite the end thereof receiving said punch member, said reduced diameter portion of said body member being press-fitted in an end of said central bore in said disk member.
 4. The punch of claim 3 wherein said reduced outer diameter portion of said body member peripherally defines on said body member a radiused shoulder portion for engagement with a correspondingly radiused portion on an end of said bore in said disk member.
 5. The punch of claim 1 wherein said punch member and said body member are made of a carbide of at least one metal.
 6. The punch of claim 3 wherein said punch member, said body member and said disk member are made of a carbide of at least one metal. 